Wick assembly for dispensing a volatile liquid from a container and method of assembling same

FIELD OF THE INVENTION

0001The application relates to dispensing systems for volatile liquids and, more particularly, to a dispensing system incorporating a porous wick.

SUMMARY OF THE INVENTION

0002According to one aspect of the invention, an interference wick assembly for dispensing a volatile liquid from a container includes a porous high density polymer wick and a plug for securement within an opening into the container. The plug includes a tapered receiver tube defining a second opening through the plug and a ridge along an inner surface of the tube. A portion of the second opening has a first dimension less than a dimension of the wick. The wick is secured within the tube by an interference fit with the ridge, and the wick has a density sufficient to develop a removal force of at least 7.22 pounds two weeks after securement within the tube.

0003According to another aspect of the invention, an interference fit wick assembly for dispersing a volatile liquid from a container includes a porous wick composed of high density polymer and having a first density and a polymeric wall defining an opening having a dimension less than a dimension of the wick. The wick is retained within the opening by a separation force caused by the interference fit, and the first density is selected such that the separation force is at least as great as a first force. The wall includes a generally frustoconical receiving member defining the opening, an insertion end having a first diameter, and a retention end having a second diameter. The first diameter is greater than the wick dimension, and the second diameter is less than the wick dimension.

0004According to yet another aspect of the invention, a method of assembling a wick assembly for dispensing a volatile liquid from a container includes the step of providing a porous wick. The wick is composed of high density polymer and has a first density. The method further includes the step of providing a generally frustoconical wall defining an opening. The wall is of a high density polyethylene and has an inner annular ridge. The opening has a dimension less than a dimension of the wick. The method also includes the step of inserting the wick into the opening. The first density is selected such that a separation force is at least as great as a first force.

0005These and other aspects of the invention will become apparent upon consideration of the detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

0006<figref idref="DRAWINGS">FIG. 1</figref> is a cross sectional view showing one embodiment of an interference fit assembly according to the present invention;

0007<figref idref="DRAWINGS">FIG. 2</figref> is a cross sectional view of the interference fit assembly of <figref idref="DRAWINGS">FIG. 1</figref> taken along line <b>2</b>-<b>2</b> in <figref idref="DRAWINGS">FIG. 1</figref>;

0008<figref idref="DRAWINGS">FIG. 3</figref> is a cross sectional view of the interference fit assembly of <figref idref="DRAWINGS">FIG. 1</figref> incorporated into a container for a volatile liquid;

0009<figref idref="DRAWINGS">FIG. 4</figref> is a cross sectional view showing a second embodiment of an interference fit assembly according to the present invention;

0010<figref idref="DRAWINGS">FIG. 5</figref> is an exploded perspective view of the interference fit assembly and container of <figref idref="DRAWINGS">FIG. 3</figref>;

0011<figref idref="DRAWINGS">FIG. 6</figref> is a schematic drawing showing the dimensions and shape of an exemplary wick.

0012<figref idref="DRAWINGS">FIG. 7</figref> is a group of drawings showing dimensions and shape of the plug member <b>306</b> of <figref idref="DRAWINGS">FIG. 3</figref>.

0013<figref idref="DRAWINGS">FIGS. 8A and 8B</figref> are a table and chart, respectively, showing the effect of increasing weight on separation force F₃.

0014<figref idref="DRAWINGS">FIGS. 9A and 9B</figref> are a table and chart, respectively, showing the effect of increasing weight on insertion force.

DETAILED DESCRIPTION OF THE INVENTION

0015Referring to <figref idref="DRAWINGS">FIG. 1</figref>, interference fit assembly <b>100</b>, in one example, comprises wall <b>102</b> and wick <b>104</b>. An interference fit couples wall <b>102</b> and wick <b>104</b> together. As shown in <figref idref="DRAWINGS">FIG. 1</figref>, wick <b>104</b> comprises a generally cylindrical first portion <b>106</b> having a first diameter d₁and a generally cylindrical second portion <b>108</b> having a second diameter d₂. Second portion <b>108</b> extends through an opening (not shown) of wall <b>102</b>. <figref idref="DRAWINGS">FIG. 1</figref> depicts diameters d₁and d₂such that first diameter d₁is greater than second diameter d₂. Alternatively, d₁is less than d₂, or d₁and d₂are the same size.

0016<figref idref="DRAWINGS">FIG. 2</figref> provides a top view of wall <b>102</b> taken along line <b>2</b>-<b>2</b> in <figref idref="DRAWINGS">FIG. 1</figref>. Wall <b>102</b> in one example forms an annular member <b>200</b>. Annular member <b>200</b> includes an opening <b>202</b>. Annular member has an interior diameter D_pwhich is defined as the diameter of opening <b>202</b>. D_pis less than diameter d₂of the second portion <b>108</b> of wick <b>104</b>. In one example, diameter d₂is 6.5% greater than D_p. In another example, diameter d₂does not exceed approximately 12% of D_p.

0017Referring to <figref idref="DRAWINGS">FIGS. 3 and 4</figref>, wick <b>104</b> is utilized to draw a liquid <b>302</b> from a container <b>304</b>. Liquid <b>302</b>, in one example, is a volatile liquid, which emits a fragrance, and container <b>304</b> is a fragrance bottle. Wick first portion <b>106</b> extends outside container <b>304</b> for immersion into either ambient air or a forced air stream. Wick second portion <b>108</b> is in communication with liquid <b>302</b>. Accordingly, liquid <b>302</b> is drawn from container <b>304</b> by wick second portion <b>108</b> and deposited into the ambient air by wick first portion <b>106</b>.

0018<figref idref="DRAWINGS">FIGS. 3 and 4</figref> disclose two embodiments for utilizing interference fit <b>100</b> to connect wick <b>104</b> to container <b>304</b>. In a first embodiment, shown in <figref idref="DRAWINGS">FIG. 3</figref>, wall <b>102</b> is incorporated into plug member <b>306</b>. Plug member <b>306</b> is adapted to be received and secured to container <b>304</b>. Plug member <b>306</b> is secured to container <b>304</b> through means, such as an interference fit, molding, adhesive, etc. In a second embodiment, shown in <figref idref="DRAWINGS">FIG. 4</figref>, wall <b>102</b> is incorporated directly into container <b>304</b>. The disclosure of the two embodiments in <figref idref="DRAWINGS">FIGS. 3 and 4</figref> is for illustrative purposes only and should not be used to limit the scope of the application to the two embodiments.

0019Referring now to <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, it should be noted that in addition to securing wall <b>102</b> and wick <b>104</b> together, interference fit assembly <b>100</b> also forms a seal to prevent leakage of liquid from the container in which wick <b>104</b> is inserted. Thus, wick second portion <b>108</b> conforms to the shape of opening <b>202</b> and substantially abuts the entire interior surface <b>204</b> of annular member <b>200</b>. In the example shown, wick second portion <b>108</b> has a generally cylindrical shape to conform to the circular shape of opening <b>202</b>. In another example, opening <b>202</b> and wick could be shaped differently; for example, if achieving a seal between wick <b>104</b> and the container in which it is inserted is not of importance.

0020In another example, wick <b>104</b> and/or opening <b>202</b> have other geometric shapes, such as hexagonal, rectangular, triangular, elliptical, etc. Detailed descriptions of wick structures are provided in co-pending patent applications having U.S. Ser. Nos. 10/266,512; 10/266,798; and 10/266,546, which are hereby incorporated by reference.

0021Wall <b>102</b> is formed from a thermoplastic material having the processing characteristics and dimensional stability needed to enable predetermined interference fit dimensional tolerances to be achieved and maintained. In one example, wall <b>102</b> is formed from a high density polyethylene, such as for example Alathon® H 5520 from Equistar Chemicals, LP of Houston, Tex.

0022Wick <b>104</b> in one example is made from material that is appropriate for its function. For example, in <figref idref="DRAWINGS">FIGS. 3 and 4</figref>, wick <b>104</b> is utilized to deliver liquid <b>302</b> from container <b>304</b> into ambient air or a forced air stream. Accordingly, wick <b>104</b> is chosen to have a predetermined range of void volume and/or pore size appropriate for providing this function. Void volume and pore size can be determined by any standard test for determining void volume and pore size distribution. For example, mercury porosimetry provides information on void volume and pore size distribution for rigid wicks. The material of wick <b>104</b> also has the processing characteristics and dimensional stability needed to enable predetermined interference fit dimensional tolerances to be achieved and maintained. In one example, wick <b>104</b> is a polymeric wick made of sintered ultra high molecular weight polyethylene (UHMW-PE). In another example, wick <b>104</b> is comprised of a blend of UHMW-PE in particle form, which is developed to meet the target pore characteristics of the wick <b>104</b>. An exemplary wick can be obtained from MicroPore Plastics Inc. of Stone Mountain, Ga.

0023The material for wick <b>104</b> is also chosen to effect a specific strength of the interference fit between wall <b>102</b> and wick <b>104</b>. <figref idref="DRAWINGS">FIG. 5</figref> shows an exploded view of the first embodiment of interference fit assembly <b>100</b>. Wick <b>104</b> is inserted into opening <b>202</b> of plug member <b>306</b>. Plug member <b>306</b> is inserted into opening <b>502</b> of container <b>304</b>. Because Diameter d₂of wick second portion <b>108</b> is larger than diameter D_pof opening <b>202</b>, an interference fit is created. To insert wick <b>104</b> through opening <b>202</b>, however, an insertion force F_Iis applied to wick <b>104</b> in the direction shown. For wick <b>104</b> to be removed from opening <b>202</b>, a separation force F_sor extraction force needs to be applied to wick <b>104</b> in the direction shown. For many applications, however, the manufacturer may not want wick <b>104</b> to be easily removed from opening <b>202</b>. For example, if interference fit assembly <b>100</b> were used as part of an air freshener, the manufacturer may not want children to be able to remove wick <b>104</b> because to do so would result in the spilling of liquid in their vicinity. Therefore, the manufacture may want the separation force F_sto be strong enough to prevent this from happening. The Applicants have discovered that both F_Iand F_sare a function of the weight of wick <b>104</b>. In particular, the density of wick <b>104</b> along and near the region of wick <b>104</b> that abuts wall <b>102</b> affects separation force F_s. The higher the density of wick <b>104</b>, the greater force that is required to both insert wick <b>104</b> into opening <b>202</b> and remove wick <b>104</b> from opening <b>202</b>.

0024Still referring to <figref idref="DRAWINGS">FIG. 5</figref>, after wick <b>104</b> is inserted into opening <b>202</b>, a period of stress relaxation occurs. Stress relaxation occurs in the materials of both wall <b>102</b> and wick <b>104</b> along and proximate the region of contact between wall <b>102</b> and wick <b>104</b>. The stress relaxation reduces the bearing force between wall <b>102</b> and wick <b>104</b> and thus F_sdecreases as a result of stress relaxation. Therefore, when determining when manufacturing interference fit assembly <b>100</b> to have a particular separation force F_s, the manufacture must take into account the effects of stress relaxation. The Applicants have found that a period of about two weeks is sufficient to allow the effects of stress relaxation to occur. After two weeks, separation force F_shas generally stabilized.

0025<figref idref="DRAWINGS">FIGS. 8A and 8B</figref>, which include Table I and Chart I, respectively, show the effect that increasing the weight, for a given volume of wick <b>104</b>, has on the separation force F, for a wall and wick after a period of about two weeks.¹In other words, Table I and Chart I show the effect that increasing the density of wick <b>104</b> has on separation force F_s. The wall <b>102</b> was made of approximately 0.9 ± 0.05 g of injection molded high density polyethylene. Wall <b>102</b> was incorporated into plug member <b>306</b> and plug member <b>306</b> was inserted into container <b>304</b> as shown in <figref idref="DRAWINGS">FIG. 3</figref>. The dimensions of wall <b>102</b>, plug member <b>306</b>, and wick <b>104</b> are provided in <figref idref="DRAWINGS">FIGS. 6 and 7</figref>. It should be noted that the dimensions provided for wall <b>102</b> and wick <b>104</b> are for illustrative purposes only. Wall <b>102</b> and wick <b>104</b> could be made larger or smaller. Provided that an interface fit is generated between wall <b>102</b> and wick <b>104</b>, the separation force F_swill increase as the density of wick <b>104</b> increases for a constant density of wall <b>102</b>. The density of wick <b>104</b> can be determined by calculating volume of wick <b>104</b> using the dimensions shown in <figref idref="DRAWINGS">FIG. 6</figref>. ¹For the weights 3.643, 3.755, 3.528, 3.629, 3.590, and 3.655 wick <b>104</b> was not separated from wall <b>102</b>. Rather, plug member <b>306</b> separated from container <b>304</b>. Accordingly, these entries list the force at which plug member was removed from container <b>304</b>.

0026<figref idref="DRAWINGS">FIGS. 9A and 9B</figref>. which include Table II and Chart II, respectively, demonstrate the effect that increasing the weight (and thereby density) of wick <b>104</b> has on insertion force for the same wall and wick as in Table I and Chart I. The tables and charts demonstrate that the higher the weight of wick <b>102</b>, the greater the insertion force F_Iand the greater the separation force F_safter stress relaxation.

INDUSTRIAL APPLICABILITY

0027The present invention provides an interference fit assembly incorporation into a container for a volatile liquid. The assembly is formed by a porous wick and a wall joined so as to generate an interference fit. The assembly forms a seal at an opening of the container to prevent leakage of the volatile liquid from the container. To help ensure that the seal remains secured in the opening of the container, the assembly is constructed such that at least a minimum threshold force is required to separate the wick from the wall. To this end, the materials and dimensions of the wick and wall are specified so as to provide a high initial engagement force between the wick and wall, and to provide maximum resistance to stress relaxation at the wick-wall interface.

0028It should be understood that the preceding is merely a detailed description of various embodiments of this invention and that numerous changes to the disclosed embodiment can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents.